I had a nice sound pop up when I got a message but after I reformatted I cant seem to figure out how O did it, I think i got it with one of these custom steam skins, does anyone know how to have a nice sound?

Would there be anyway to edit it so that I could say, create a list of sounds for friend_online and have Steam randomly pick a unique sound each time? I'm sick of hearing the same sound and don't want to change it so often. I would love this.